This invention relates to bearings of steam turbines and other rotary machines of a large size, and more particularly it is concerned with a method of diagnosis of the operating conditions of a bearing and an apparatus therefor capable of making accurate diagnosis of the operating conditions of the bearing.
As is well known, a rotary machine of a large size, such as a steam turbine, includes a multispan shaft system rotatably supported by a series of journal bearings. In a rotary machine of the type described, the static flexure of the shaft becomes not negligible when the rigidity of the shaft is lowered. At the same time, the shaft tends to develop unstable vibration, such as an oil whipping, because the shaft operates in a range of rotational velocities over twice the primary critical velocity. To avoid such unstable vibration, it is the present practice to increase the surface pressure of the bearings. Thus, in a multispan shaft system, the upper limit of the load on the bearings with respect to seizure and the lower limit of the load on them with respect to unstable vibration are measured, and alignment is set for each bearing in such a manner that the load applied thereto is within the aforesaid range of tolerances. As a result, the line connecting together the centers of the bearings is not straight, and the centers of the bearings have heights which may vary depending on the amount of static flexure due to a variation in the rigidity of the shaft. In this case, each bearing is deflected to conform to the deflection of the shaft.
Thus it is essential that the operating conditions of each bearing be placed under surveillance to determine whether or not the bearing follows up any change which might occur in the shaft. Particularly in a large rotary machine in which reliability of performance is an important factor, it is essential that the operating conditions of each bearing be accurately sensed and indicated.
U.S. Pat. No. 4,118,933 is a prior art reference directed to a bearing load indicator which functions to sense, indicate and/or record loading on a bearing. This prior art reference uses strain gauges disposed on the bearing support yoke for detecting the load on the bearing based on changes in the resistance of the strain gauges.